The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A piston installed at each of cylinders of an engine reciprocates between a predetermined top dead point and a bottom dead point to compress air or a mixture introduced into each of the cylinders.
Conventionally, in the engine, a crankshaft, the connecting rod, and the piston are formed in predetermined shapes and are connected to one another at fixed positions, so that they have a fixed compression ratio. Since the compression ratio is fixed, an output of the engine is inevitably controlled by air and fuel.
There is provided a variable compression device for varying a compression ratio by varying positions of upper and lower limits of the piston in each of the cylinders.
As an example of the variable compression device, an angle of an eccentric cam installed at a portion at which a connecting rod and a piston are connected is varied using a hydraulic pressure such a position of the piston is varied and thus a compression ratio is varied.
However, we have discovered that in the variable compression apparatus according to a related art, as oil is compressed by a force applied to the piston, a volume of an oil chamber for storing the oil is changed and thus a position of the piston is varied such that a predetermined compression ratio cannot be maintained.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the present disclosure, and therefore it may contain information that does not form the prior art that is already known to a person of ordinary skill in the art.